1. Field of the Invention
The present invention relates to a thrust vectoring variable geometry exhaust nozzle for gas turbines, especially intended for gas turbines used as the means of propulsion in aviation.
More particularly, the exhaust nozzle of the present invention is of the axisymmetric type consisting of a convergent section followed, in the direction of the flow, by a divergent section, both formed from master petals arranged circumferentially about the centerline of the turbine to define a thrust exhaust duet and connected to each other by cylindrical linkage having axes perpendicular to the centerline of the turbine and slave petals also connected to each other by cylindrical linkages. The convergent section defines a throat of variable area and the divergent section has a variable geometry in order to orientate the thrust in any direction on a theoretical cone located around the centerline of the turbine.
2. Description of the Related Art
The maneuverability of aircraft is an essential and important factor. This maneuverability, which to date has been achieved by aerodynamic forces, can be substantially improved by modifying the vectoring of the thrust of the nozzle starting from its normal axial direction of action.
The vectoring of the thrust of exhaust nozzles has for many years been used in rocket engines. There the systems are much simpler since the exhaust nozzles have constant geometry.
Variable geometry convergent-divergent exhaust nozzles have only been recently introduced in supersonic aircraft powered by turboreactor or turbofan engines. In this class of exhaust nozzles, the vectoring systems for the thrust are still not in an operational state, but are only at the research and development phase. Those that are at a more advanced phase are the bidimensional type, in which the thrust is orientated solely in one plane.
Carrying out the vectoring of the thrust in exhaust nozzles with axial symmetry has a special advantage, since the direction of the thrust can be varied in any axial plane, the pitch and yaw planes being particularly important.
Several patents exist on mechanisms for vectoring of the thrust in this class of exhaust nozzles, since it theoretically possible to carry this out in various ways, although it is very difficult to ensure that there are no major complications. U.S. Pat. No. 4,994,660 and European Patent No. 281,264 describe vectoring mechanisms for the thrust in exhaust nozzles of this class and their systems of action, and furthermore, describe the special advantages shown by these mechanisms in comparison with the other known systems.
The most commonly applied mechanism for creating a variable geometry axisymmetric convergent-divergent exhaust nozzle, as can be seen in different turbines currently in operation or being developed, consists of a convergent section comprising a plurality of convergent master petals, interleaved among which are convergent slave petals for sealing the free spaces or interstices between neighboring master petals. Beyond this convergent section is a divergent section consisting of the same plurality of divergent master petals interleaved among which are a plurality of divergent slave petals for the sealing. The upstream end, according to the direction of the gas flow, of each divergent master petal is joined by means of a linkage to the convergent master petal, with which it forms a pair. The divergent master petal in turn is joined at a point intermediate its downstream end to the downstream end of a strut, by means of a spherical linkage. The upstream end of each convergent master petal and that of each strut are joined by means of cylindrical linkages to a rigid structure which normally forms part of the post-combustion housing of the turbine. The variation in the area of the throat A8 is achieved by means of a roller which is pulled by a ring that is moved axially and is governed by a plurality of actuators connected to it via spherical linkages and which act on a cam which in turn forms an integral part of the convergent master petal.
It has been well known in the prior art, in fields such as mining, to use a water cannon to deviate the hydraulic jet omindirectionally. The water cannon consists of a fixed tube upstream and another tube with a conical extension located downstream. The tubes are interconnected by means of a spherical bearing or a universal-type bearing that allows the conical tube to be orientated with respect to the fixed tube. When dealing with powerful hydraulic cannons, the vectoring of the conical tube is done by a system of at least three bars which, arranged around the tube, interlink the downstream projecting end of the tube to the external ring of the universal bearing, so that when this is inclined, the corresponding orientating transverse force is transmitted to that projecting end.
Moreover, in recent decades in the field of turbopropulsion turbines, certain vectoring systems for the thrust have been proposed and developed. All these systems can be classified into three major groups, i.e.:
1) Those which orientate the whole exhaust nozzle upstream of the throat. PA1 2) Those which orientate the divergent part of the exhaust nozzle, i.e., the whole part located immediately downstream of the throat. PA1 3) Those which orientate the flow at the outlet or somewhat more downstream of the outlet of the exhaust nozzle.
Orientating the whole exhaust nozzle upstream of the inlet section has the drawback that the perturbations induced by the vectoring are transmitted upstream of the turbine and require a highly complicated sealing device for the interstices between the different mobile components.
The sealing of these interstices is simplified in the case of exhaust nozzles orientable from their throat section. Even so, a seal needs to be provided for the slot formed between one flat convergent petal and its pair, the divergent petal, also being flat with which it is linked via a spherical bearing.
Moreover, during vectoring, the geometry of the longitudinal interstices between adjacent divergent petals alters, which corresponding approximately to that of a rectangle, becomes that of a ruled surface whose sides cease to be parallel. In order to prevent such a distorted geometry in the slot, a solution is shown by U.S. Pat. No. 4,994,660, consisting of a dorsal bar on which is mounted a plurality of segments that can rotate around that bar. Although this solution solves the problem of sealing the slot, the set of segments constitutes a very rough wall with a multitude of ridges transverse to the direction of the flow.
In the case of exhaust nozzles fitted with flow orientators at the outlet, the resulting system is very heavy and voluminous.
A characteristic of all the known vectoring systems is the presence of the two independently acting systems, one to vary the geometry of the throat and that of the outlet axisymmetrically, and another to orientate the supporting struts at the downstream end of the divergent petals, as explained in U.S. Pat. No. 4,994,660. Although such an exhaust nozzle has the flexibility for optimizing the law of ratios between the throat area and the outlet area and can accommodate itself to changes for different requirements, the system suffers from complexity, mass and cost.